I mean I'm still on GCSEs but in year 10 I was failing English Lit and getting lower than 50% in any essay or test we did on past papers and I worked insanely hard at it and jumped to above 80% in a term and I'm really proud to say I got 98% in my mock. With my motivation, I just kept comparing myself to my mates who were getting good grades and my motivation was that I wanted to be the mate who was always getting the better mark (toxic I know...but it works and my friends and I think its funny). It also helps to compare yourself to the people you hate with bad grades because the 'I don't wanna be like then' mentality is quite empowering somehow.